Qualitative and quantitative changes in stored rice

Abstract

Qualitative and quantitative changes in stored rice varieties viz. PTB – 10 and Red Thriveni were determined by assuming the changes in their grain constituents, physical characteristics, insect infestation, cooking characteristics and organoleptic qualities. After six months storage effect of different storage containers such as gunny bag, pathayam and metal bin on these qualities were taken into consideration.

The grain constituents like protein, nonprotein nitrogen, calcium , iron and phosphorous were found to decrease at a greater rate in PTB – 10 stored in gunny bag when compared to red thriveni. Similarly constituents like moisture, uric acid and freefatty acids were found to increase in PTB-10 than in red thriveni.

Chnages in grain constituents, reducing sugars, nonreducing sugars, starch and amylose were observed both in raw as well as in cooked rice samples after storage. Increase in reducing sugar and amylose was at a greater rate in PTB-10 stored in gunny bag especially when cooked while nonreducing sugars and starch level were found to decrease in a similar order.

Compared to PTB – 10 in gunny bag after storage, red Thriveni obtained lower values for thousand grain weight and total solid level, when stored in all the storage containers tried. Head rice yield and gelatinization temperature of rice samples increased in red thriveni after storage, the rate being higher in gunny bag when compared to other two storage structures. Viscosity was found to increase greatly in red thriveni stored in metal bin.

Insect infestation was found to be greater in gunny bags while metal bin was found to be insect proof. PTB – 10 was affected by insects more when compared to Red thriveni. PTB-10 obtained higher values for cooking characteristics such as volume expansion and gruel loss than red thriveni, when stored in gunny bag. As as result of storage water uptake level and swelling index increased at a greater rate in red thriveni in all the storage containers tried. The rate of decrease in optimum cooking time was greater in PTB-10 stored in gunny bag while stickness was greatly reduced in red thriveni when compared to PTB-10. Raw rice samples were more acceptable before storage as quality parameter hardness increased after storage. Storage provided low scores for colour and odour which had a negative influence on consumer acceptance.

Red Thriveni was more acceptable for all the quality attributes than PTB-10. The quality attributes colour and appearance obtained low scores in the two rice varieties the decrease being greater in PTB-10 than Red Thriveni. Taste, flavor and doneness was found to decrease in the two rice samples. The rate of decrease in taste. Flavor and doneness was lower in red thriveni when compared to PTB-10. Among the storage containers, metal bin was found to be a better storage structure than pathayam and gunny bag.

The experiment threw light on the significant of metal bin as a storage structure and favourable facts in the shelf life qualities of evolved varieties like red thriveni.